Image display systems based on spatial light modulators (SLMs) are an alternative to image display systems that are based on cathode ray tubes (CRTs). SLM systems provide high resolution without the bulk of CRT systems.
Digital micro-mirror devices (DMDs) are one type of SLM, and may be used for either direct view or for projection displays. A DMD has an array of hundreds or thousands of tiny tilting mirrors, each of which provides light for one pixel of an image. To permit the mirrors to tilt, each mirror is attached to one or more hinges mounted on support posts, and spaced by means of an air gap over underlying control circuitry. The control circuitry provides electrostatic forces, which cause each mirror to selectively tilt. For display applications, image data is loaded to memory cells of the DMD and in accordance with this data, mirrors are tilted so as to either reflect light to, or deflect light from, the image plane.
One approach to providing color images in an SLM display system is referred to as "sequential color". All pixels of a frame of the image are sequentially addressed with different colors. For example, each pixel might have a red, a green, and a blue value. Then, during each frame period, the pixels of that frame are addressed with their red, blue, then green data, alternatingly. A color wheel having three segments of these same colors is synchronized to the data so that as the data for each color is displayed by the SLM, the light incident on the SLM is filtered by the color wheel. For standard display rates, such as the 30 frame per second NTSC rate, the eye perceives the image as having the proper color.
Various modulation schemes can be used to vary the intensity of each color. For example, each pixel might have a 24-bit value, 8 bits for each color. This permits 2.sup.8 =256 levels of intensity for each color, which includes a 0 value for no color (black). Then, for each color, the pixel can be on for a length of time for corresponding to its pixel value, and the combination of colors can provide a full color display.
For color displays, one aspect of picture quality is color temperature. This is a subjective evaluation, indicated by the "whiteness" of white. It is assumed by analogy to the photographic film industry, that color temperature preferences follow certain geographic patterns. For example, Americans seem to prefer a bluish white color temperature. Europeans seem to prefer whatever color temperature provides a "truest" skin tones. It is desirable for a color display system to be able to provide whatever color temperature is preferred in a given market.